#include <assert.h>
#include <stdio.h>
#include <string.h>

#include "houdini.h"

#define ESCAPE_GROW_FACTOR(x) (((x) * 12) / 10)

/*
 * The following characters will not be escaped:
 *
 *      -_.+!*'(),%#@?=;:/,+&$ alphanum
 *
 * Note that this character set is the addition of:
 *
 *  - The characters which are safe to be in an URL
 *  - The characters which are *not* safe to be in
 *  an URL because they are RESERVED characters.
 *
 * We asume (lazily) that any RESERVED char that
 * appears inside an URL is actually meant to
 * have its native function (i.e. as an URL
 * component/separator) and hence needs no escaping.
 *
 * There are two exceptions: the chacters & (amp)
 * and ' (single quote) do not appear in the table.
 * They are meant to appear in the URL as components,
 * yet they require special HTML-entity escaping
 * to generate valid HTML markup.
 *
 * All other characters will be escaped to %XX.
 *
 */
static const char HREF_SAFE[] = {
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 1, 0, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 0, 1,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1,
    0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
};

void
houdini_escape_href(struct sd_buf *ob, const uint8_t *src, size_t size)
{
    static const char hex_chars[] = "0123456789ABCDEF";
    size_t  i = 0, org;
    char hex_str[3];

    sd_bufgrow(ob, ESCAPE_GROW_FACTOR(size));
    hex_str[0] = '%';

    while (i < size) {
        org = i;
        while (i < size && HREF_SAFE[src[i]] != 0)
            i++;

        if (i > org)
            sd_bufput(ob, src + org, i - org);

        /* escaping */
        if (i >= size)
            break;

        switch (src[i]) {
        /* amp appears all the time in URLs, but needs
         * HTML-entity escaping to be inside an href */
        case '&':
            SD_BUFPUTSL(ob, "&amp;");
            break;

        /* the single quote is a valid URL character
         * according to the standard; it needs HTML
         * entity escaping too */
        case '\'':
            SD_BUFPUTSL(ob, "&#x27;");
            break;

        /* the space can be escaped to %20 or a plus
         * sign. we're going with the generic escape
         * for now. the plus thing is more commonly seen
         * when building GET strings */
#if 0
        case ' ':
            sd_bufputc(ob, '+');
            break;
#endif

        /* every other character goes with a %XX escaping */
        default:
            hex_str[1] = hex_chars[(src[i] >> 4) & 0xF];
            hex_str[2] = hex_chars[src[i] & 0xF];
            sd_bufput(ob, hex_str, 3);
        }

        i++;
    }
}
